1. Field of the Invention
This invention relates generally to aerodynamic drogues for aerial inflight refueling, and more particularly concerns an improved drogue having adjustable support arms for a canopy to permit the configuration of the drogue to be modified in flight to be useful at different air speeds.
2. Description of Related Art
The development of drogues for inflight refueling of aircraft has been primarily directed by the need to stabilize a refueling hose trailing from a tanker aircraft in a generally horizontal attitude. The drogue provides drag for the refueling coupling, which must resist the forward movement of a probe from a refueling aircraft. Cone shaped drogues have proved to be suitable for low speed inflight refueling; however, it has been found that such drogues can generate excessive drag at higher speeds, creating loads beyond the hose reel operating capabilities.
The high amount of drag provided by a drogue for low speed refueling also can cause the trail angle of the refueling hose and coupling to become flattened. It is desirable that the refueling aircraft not follow directly in the wake of the tanker aircraft, because the configuration of a drogue which may be appropriate for low air speed refueling can be inappropriate for high speed refueling, even if the motion of the refueling coupling can be stabilized by aerodynamic designs.
It has therefore been a common practice to install either a low or high speed configuration drogue on the refueling coupling of a tanker aircraft on the ground, depending upon whether the aerial refueling is to take place at low or high speed, and to land to change the drogue to one of another speed configuration when an aircraft needs to be refueled at a different speed. Another approach has been to fabricate the ring shaped parachute canopy of the drogue of elastic material with openings which permit pressure modulation to provide for a constant amount of drag over varying speeds. However, such elastic openings have been found to be subject to deterioration, which can cause the amount of drag provided by the drogue to decrease over time, and can also cause an asymmetrical drag configuration to develop.
It has also been proposed to mount the ring shaped canopy to a spring assembly allowing for deflection of the canopy of the drogue to provide for a constant amount of drag, so that the drogue can be used at varying speeds. Such a spring mounting of the canopy at the trailing edge of the fuel coupling or support arms has also been found to be prone to damage from contact with a probe of a refueling aircraft, which can interfere with the drag configuration and stability of the drogue during the inflight refueling operation.
There is therefore a continuing need for a variable speed drogue which can be modified during flight or on the ground to have different drag configurations to allow the drogue to be used at high and low speeds, and which is not generally susceptible to deterioration or damage from a refueling probe. In order to safely control the amount of drag provided by the drogue, it would be desirable to be able to adjust the projected area of the canopy of the drogue in flight by a mechanism external to the fuel coupling for changing the angle of separation of support arms to which the canopy is attached. It would be also be desirable that the support arms be external to the fuel coupling, to be generally protected from potentially damaging contact with a refueling probe. Where the canopy is attached to a series of leading and trailing edge support arms, it would also be desirable to provide a mechanism for uniformly and symmetrically moving the pivot points of the leading edge support arms relative to the trailing edge support arms, to change the projected area of the canopy, and to consequently adjust amount of drag of the refueling drogue for operation at different speeds. It would further be desirable that the drag adjustment mechanism be operable remotely or manually, during flight or on the ground. The present invention fulfills these needs.